60 GENERAL ORNITHOLOGY. 
What is a Bird ?— There is every reason to believe that a Bird is a greatly modified 
Reptile, being the offspring by direct descent of some reptilian progenitor; and there is no 
reason to suppose that any bird ever had any other origin than by due process of hatching out 
of an egg laid by its mother after fecundation by its father, —just what we believe to have been 
the invariable method during the period of the world known to human history. There is no 
reason to believe that any bird was ever originally created and endowed with the characters it 
now possesses; but that every bird now living is the naturally modified lineal descendant 
of parents that were less and less like itself, and more and more like certain reptiles, the 
further removed they were in the line of avian ancestry from such birds as are now living. 
This is the Darwinian logic of observed facts, upon which the modern Theory of Evolution is 
based,*in opposition to the tradition of the special creation of every species of animal; which 
latter has no scientific basis whatever, and is consequently accepted as true by few thought- 
ful persons who are capable of forming independent judgments. . Accordingly, 
Birds and Reptiles—even those of the present geologic epoch — share so many and so 
important structural characters, that the chiefs of science of our day are wont to unite the two 
classes, Aves and Reptilia, in one primary group of the Vertebrata, or animals with a back- 
bone. This group is called Sawropsida, or reptiliform ; it is contrasted, on the one hand, with 
Ichihyopsida, or fish-like vertebrates, including Batrachians as well as Fishes; and, on the 
other, with Mammalia, the province of the Vertebrata which includes Man and all other 
animals that suckle their young. We find that . 
The Sauropsida (Gr. catpos, sawros, a reptile; dys, opsis, appearance), or lizard-like 
Vertebrates, agree with one another, and differ from other animals, in the following important 
combination of characters, substantially as laid down by Professor Huxley, — some of the char- 
acters being shared by the Ichthyopsida, and some by the Mammalia, but the sum of the 
characters being distinctive of Sawropsida: They are all oviparous (laying eggs hatched out- 
side the body of the parent), or ovoviviparous (laying eggs hatched inside the body of the 
parent), being never viviparous (bringing forth alive young nourished before birth by the 
blood of the mother). The embryo develops those foetal organs called amnion and allantois, 
and is nourished before hatching by the great quantity of yolk in the egg. There are no 
mammary glands to furnish the young with milk after birth. The generative, urinary, and 
digestive organs come together behind in a common receptacle, the cloaca, or sewer, and their 
products are discharged by a single orifice. The kidneys of the early embryo, called Wolffian 
bodies, are soon replaced functionally by permanent kidneys, and structurally by the testes of 
the male and the ovaries of the female. The cavity of the abdomen, or belly, is not separated 
from that of the thorax, or chest, by a complete muscular partition, or diaphragm. The great 
lateral hemispheres of the brain are not connected by a transverse commissure, or corpus 
callosum. Air is always breathed by true lungs, never by gills. The blood, which may be 
cold or hot, has red oval nucleated corpuscles; the heart has either three or four separate 
chambers, — the latter in birds, in which the circulation of the hot blood is completely double, 
z.é., in the lungs and one side of the heart, in the body at large and the other side of the heart. 
The aortic arches are several ; or if but one, as in birds, it is the right, not the left. as in mam- 
mals. The centra, or bodies, of the vertebrae are ossified, but have no terminal epiphyses. 
The skull hinges upon the back-bone by a single median protuberance, or condyle, and the 
part bearing the condyle is completely ossified. The lower jaw consists of several separate 
pieces, the articular one of which hinges upon a movable quadrate bone; and there are 
other peculiarities in the formation of the skull. The ankle-joint is situated, not, as in 
mammals, between the tarsal bones and those of the leg, but between two rows of tarsal bones. 
The skin is usually covered with outgrowths, in the form of scales or feathers. — Different as 
